The Centers for Disease Control and Prevention (CDC) on Sunday formally accepted the recommendation from its advisory panel that Johnson & Johnson's COVID-19 vaccine can be given to people ages 18 and older in the United States. The announcement by CDC Director Rochelle Walensky will allow vaccinations to begin as soon as the doses are received. Walensky called the decision "another milestone toward an end to the pandemic."

"This vaccine is also another important tool in our toolbox to equitably vaccinate as many people as possible, as quickly as possible," Walensky said in a statement.

A senior administration official told reporters Sunday evening that Johnson & Johnson will ship 3.9 million doses immediately, and vaccine distribution centers will start receiving them as early as Tuesday.

Experts have said the vaccine could be targeted at places like rural communities, health centers or individual physician offices because of its relatively easy storage requirements.

However, senior administration officials said the goal is equitable distribution, and doses will be allocated to states by population, just as the vaccines from Pfizer-BioNTech and Moderna are.

Most communities will have doses of all three vaccines, but not every vaccination site will because of limited availability. Officials stressed people should take whatever vaccine is available.

An administration official said the 3.9 million doses are Johnson & Johnson's entire inventory. There will not be any additional deliveries next week, and the official said governors are aware distribution through the early and middle parts of March will be "uneven."

A total 20 million doses of J&J's vaccine will be sent in March, but they will be concentrated more toward the end of the month. The U.S. has paid for 100 million doses, which the company has pledged will be delivered by June.

The U.S. paid more than $1 billion to aid in the manufacturing and delivery of J&J's vaccine. Nearly a year ago, the company also won $465 million in federal funding for vaccine research and development, bringing its U.S. funding total on the project to almost $1.5 billion.

The nation's third coronavirus vaccine arrives days after the United States surpassed 500,000 COVID-19 deaths.

While nursing home deaths have sharply dropped, as have overall cases and deaths, the CDC is warning the decline in new cases has stalled amid a rise in more contagious variants of the virus.

At the same time, governors across the country are lifting coronavirus restrictions, including mask mandates and capacity limits, despite warning signs of a new spike from the virus mutations.

"This third safe, effective COVID-19 vaccine comes at a potentially pivotal time," Walensky said in the statement.

"CDC’s latest data suggest that recent declines in COVID-19 cases may be stalling and potentially leveling off at still very high numbers. That is why it is so critical that we remain vigilant and consistently take all of the mitigation steps we know work to stop the spread of COVID-19 while we work our way toward mass vaccination," Walensky said.